Projectors and other similar devices project an image onto a screen or the like. In one application of projectors, the positions of a projection surface and the projector as well as the image size are adjusted so that an actual-size image of an object is projected, thereby giving a user the true sense of the size of the object whose image is being projected.
In Patent Literature 1, there is disclosed a projection display system configured to acquire a distance to a projection surface that is optimum for a projector and change the size of an image of an object so that the object image projected on the projection surface at the optimum distance has the actual size of the object. The system further checks the actual distance to the projection surface and displays a message that informs of a difference between the actual distance and the optimum distance, thereby allowing for manual adjustment of the distance between the projection surface and the projector so as to reduce an error in the size of the projected image of the object.